Rudy, Dave,
     
     I concur with the flatness issue. Have seen several customers request 
     "no reflow" to achieve flat pads without changing their processes to 
     accommodate for gold or OSP's. I would believe Rudy's comment to be 
     true about requiring a more aggressive flux being needed to activate 
     the surface. I have also had customers request a minimal thickness of 
     plated tin/lead unfused on an MCM-L. They were "pasting" the pads, 
     which were in fact becoming the lead-frame attachments for a QFP, with 
     a higher temp solder (90/10 I think). This is so that the frame would 
     withstand the subsequent solder operations when the MCM-L is mounted 
     on the PWB. 
     
     Regards, 
     
     Tom


______________________________ Reply Separator _________________________________
Subject: Re: Unfused Solder and/or Tin
Author:  [log in to unmask] at INTERNET_GATEWAY
Date:    10/17/96 11:18 AM


Rudy,
     
I believe the primary reason is that it is Flat.  Finish flatness is 
critical to many SMT component placements and if the assembler can solve 
the other issues you mention they might have a winner. I do know a 
company that customer was requesting a very thin unfused tin-lead plate 
for flatness issues.
     
Regards
__________________________________________________
     
David W. Bergman, V.P. of Technical Programs 
IPC
2215 Sanders Road
Northbrook, IL  60062-6135
847-509-9700 x340 Phone
847-509-9798 Fax
email  [log in to unmask]
www  http://www.ipc.org
faxback support 800-646-0089
---------------------------------------------------
     
     
On Thu, 17 Oct 1996 [log in to unmask] wrote:
     
> Recently had occaision to have some problems associated with recovering
> scrapped PCB's that have as final finish UNFUSED plated Tin or Solder (wasn't 
> sure which).  Is there anyone who can enlighten me as to why an
> assembler/user would want such a finish.  The finish oxidizes heavily, and 
> quickly, and I suspect likely needs to be cleaned immediately before
> soldering, or alternately requires a flux so active that it will etch the 
> substrate if not washed off in a few minutes....
> 
> Other than that, it is likely wonderful?? 
> 
> Can anyone help me understand this strange (to me) finish? 
> 
> Rudy Sedlak
> 
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